rsa encryption in c continued

/* johnpfeiffer 2011-08 example rsa - it requires: gcc -o outputbinary inputfile.c -lm */

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <math.h>

int main( int argc , char* argv[] )
{
    int primeA = 3 ,  
          primeB = 11 , 
          privatekeyphi ,
          publickeymodulo , 
          publickey ,
          privatekey ,
          plaintext =7 ,
          encryptedtext ;

    /* the modulus for both public & private keys should have very few factors */
    publickeymodulo = primeA * primeB;  
    privatekeyphi = ( primeA - 1 ) * ( primeB - 1 );
    publickey = 3 ;  /* picked such that: phi is coprime (not divisble by publickey), and 1 < publickey < phi */

    printf( "%d is a secret prime \n" , primeA );
    printf( "%d is a secret prime \n" , primeB );
    printf( "%d is primeA * primeB = public modulus\n" , publickeymodulo ) ;
    printf( "%d is (primeA - 1) *( primeB - 1 ) = secret phi \n" , privatekeyphi );
    printf( "pick publickey such that it is coprime of phi and 1 < publickey < phi \n" );   
    printf( "%d is the Public Key (coprime to phi and the 'exponent') \n" , publickey );

    /*     
    to create a remainder of 1  ...
    (e * d) % (phi) = 1;    
    (7 * d ) % 20 = 1   ... e.g. d = 3         
    d = pow( e , -1 );
    */

    privatekey=1;
    while( ((publickey * privatekey) % privatekeyphi ) != 1 )
    {
      printf( "%d\n ", privatekey);
      privatekey++ ; 
    }

  printf( "%d is the Private Key \n" , privatekey );

  printf( "sender uses encrypted = (plaintext) ^ e \n" );

  encryptedtext = (int) ( pow( plaintext , publickey ) ) % publickeymodulo ;

  printf( "%d encrypted becomes %d \n" , plaintext , encryptedtext );


  plaintext = (int) ( pow( encryptedtext , privatekey ) ) % publickeymodulo ;

  printf( "  plaintext = (int) ( pow( encryptedtext , privatekey ) ) mod publickeymodulo ; \n");
  printf( "%d decrypted becomes %d \n" , encryptedtext , plaintext );

  return 0;

}/* end main */